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Poster — Wed Eve—36: Preliminary Results of Patient Scatter Model for EPID Dosimetry
Author(s) -
Chytyk K,
McCurdy BMC
Publication year - 2009
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3244140
Subject(s) - dosimetry , image guided radiation therapy , imaging phantom , monte carlo method , nuclear medicine , radiation therapy , fluence , medical imaging , radiosurgery , beam (structure) , radiation treatment planning , medical physics , optics , physics , medicine , radiology , mathematics , statistics , laser
Complex radiotherapy techniques, such as intensity modulated radiation therapy (IMRT) or volumetric modulated radiation therapy (VMAT), have greatly increased the motivation for dosimetric verification of radiation therapy treatments. Pretreatment dosimetry is typically carried out prior to a patient's treatment but verification of the actual delivered treatment is not usually performed. Amorphous silicon electronic portal imaging devices (a‐Si EPIDs) have been established for IMRT verification, with one method involving the comparison of a predicted image to a measured image to determine whether the treatment field was delivered correctly. In this work, a comprehensive physics‐based parameter fluence model is interfaced with a patient scatter model to predict portal dose images. The patient scatter algorithm consists of a library of Monte Carlo calculated, scattered photon fluence kernels which predict scattered energy fluence exiting the patient or phantom. Images were acquired with an a‐Si EPID using a 6 MV beam and slab material in the beam path to test the model. Field size ranged from 1×1 to 20 × 20cm 2 , with solid water thicknesses extending from 1 cm to 25 cm and an air gap of 40 cm. A prostate IMRT field was acquired during a patient treatment for prediction as well. Smaller fields were found to be accurately predicted within 2% and 2 mm, while larger fields were over‐predicted. The prostate field agreed within 2%, 3 mm. The model is able to accurately predict most MLC‐defined fields to within 2% and 2 mm; a prostate IMRT field has also been accurately predicted.